1. Field of Invention
The present invention relates to a recording medium detection method for detecting if a recording medium having peelable labels affixed at a regular interval on the surface of a continuous liner is present in the transportation path of a label printer, for example. More particularly, the invention relates to a recording medium detection method and a label printer that can accurately determine if the recording medium is present or not using a reflection photosensor and a transmission photosensor.
2. Description of Related Art
Label printers convey a recording medium having peelable labels affixed at a regular interval on the surface of a continuous liner passed the printing position of a print head to print the individual labels. A reflection photosensor or a transmission photosensor for detecting the labels is disposed to the transportation path upstream from the printing position in the transportation direction in order to enable printing the labels correctly.
A reflection photosensor detects black marks that are preprinted at regular intervals on the liner to indicate the position of each label. These black marks are printed near the edge of the liner on the downstream side of each label in the transportation direction. When a black mark is at the detection position of the photosensor, the reflection is not detected. If a part of the liner where a black mark is not printed is at the detection position, the reflection is detected.
A transmission photosensor detects each label. If a label is at the detection position of the transmission photosensor, light transmission is not detected. If only the liner between adjacent labels is at the detection position, light transmission is detected.
Japanese Unexamined Patent Appl. Pub. JP-A-2000-71548 teaches a label printer that has both reflection and transmission photosensors. The photoreceptor or photoemitter of the reflection photosensor or transmission photosensor is mounted on one sensor circuit board, and the detection position of the opposing reflection photosensor or transmission photosensor is disposed to the same location in the transportation direction.
With the detection method taught in JP-A-2000-71548, the reflection photosensor will not detect reflected light and the transmission photosensor will not detect the emitted light if there is no recording medium in the transportation path. Some recording media, however, have a transparent liner or have holes or perforations in the liner. If only the liner part of such a recording medium is at the detection position of the reflection photosensor and the transmission photosensor, reflection will not be detected but transmission will be detected, and the photosensor output will be the same as when there is no recording medium in the transportation path. As a result, it will be incorrectly detected that the recording medium is not present even though the recording medium is in the transportation path, and printing will not proceed.
To avoid such detection errors, the label printer could execute the operation that conveys the recording medium a predetermined distance before printing starts, and determine that there is no recording medium in the transportation path if reflection is not detected and there is no change in the transmission detection status during this transportation operation. However, if this method of executing the operation that conveys the recording medium before printing starts to determine if the recording medium is in the transportation path is used, the startup time of the label printer takes longer and usability drops.